桃小食心虫病原菌—球孢白僵菌TST05菌株生物学特性研究

[目的]研究从自然染病的桃小食心虫幼虫上分离的球孢白僵菌TST05菌株的生物学特性.[方法]测定不同培养基、外界不同温度和湿度对该菌株菌丝营养生长及孢子萌发的影响.[结果]该菌株在PDA、PPDA、SDAY、SMAY 4种培养基上均生长良好,菌落厚而致密,产孢量均大于3.95×107孢子/mL;菌株适应的温度和湿度范围宽,15～30℃之间,RH 30 ％～100％之间孢子均可萌发、生长和产孢.随着温度接近25℃、湿度增大,孢子的萌发率、菌落的生长速率和产孢量都显著增加.15℃、RH 100％时产孢量为1.32× 107孢子/mL;25℃、RH 30％时,产孢量也能达到1.37×107孢子/mL;25℃、RH 100％时产孢量达到6.19×107孢子/mL.15℃、RH 100％孢子萌发率为52.28％;25℃、RH＞80％时,孢子萌发率都能达到90％以上.[结论]TST05菌株能适应北方干旱低温条件,可开发成为防治桃小食心虫的生物制剂.     

Influence of environmental conditions in a glasshouse on conidia ofBotrytis cinerea and on post-harvest infection of rose flowers

Quantification and horizontal distribution of air-borne inoculum ofBotrytis cinerea in a rose crop in a glasshouse of 300 m² was studied in 1991 and 1992. Conidia ofB. cinerea were caught in spore traps consisting of an agar medium selective forB. cinerea in Petri dishes placed within the crop, at flower height 1 m above the ground. Spore catches were counted as colonies, after incubation. Lesions due to conidial infection were counted on petals of rose flowers, also after incubation. Relative humidity (RH) and temperature within the glasshouse and global radiation and windspeed outside were recorded during the experiments. The horizontal distribution ofB. cinerea in a rose crop grown under glass was fairly uniform in both years. In 1991 a clear seasonal pattern in the number of colonies could not be found. In 1992 the number of colonies were high in August, September and October. The number of lesions on rose flowers showed a distinct pattern in both years. In August, September and October many lesions were counted whereas in the other months few lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 76 and 63% of the variation in the number of lesions on rose flowers in 1991 and 1992, in terms of relative humidity (positively correlated), global radiation outside the glasshouse (negatively correlated) and, numbers of colonies on spore traps (positively correlated). The results in the rose crop suggest that RH, global radiation and spore density in glasshouses are important variables in regulating the numbers of lesions during storage and transport. The numbers of spores in glasshouses are dependent on the production system. A glasshouse with a system resulting in wet dead tissue on the ground give higher amount of spores in the glasshouse air and through that high numbers of lesions on flowers. On roses outside the glasshouses very high numbers of lesions were counted sometimes, mostly during and after rain showers, as a result of rain-deposition of spores onto the flowers.     

湿度调控对番茄灰霉病菌侵染的影响

 番茄灰霉病菌(Botrytes cinerea)的分生孢子萌发需要高湿的环境,一般要求相对湿度在80%以上或水滴中萌发最好。在适温下,随着湿度的增加,病菌致病性增强,孢子在相对湿度85%以上、菌丝在相对湿度80%以上的高湿环境能够发生侵染,并形成危害性的软腐斑。在一天中高湿的时间直接影响番茄灰霉病的发生,高湿(相对湿度超过85%)时间8h以上病菌才能够连续侵染。     

Storability of onion bulbs contaminated by<Emphasis Type="Italic">Aspergillus niger</Emphasis> mold

In the course of pre- and postharvest epidemiological studies on bulbs contamination byAspergillus niger, two Sudanese onion cultivars were tested: ‘Saggai Red’ and ‘El-Hilo White’.A. niger spores, whether seedborne, soilborne or airborne, were avirulent to the healthy growing onion plants. The fungus heavily contaminated the dead onion tissues, mainly the dead leaves followed by the dry scales, the dead roots and, to a lesser extent, the bulb necks, preferring the red-skinned cultivar to the white one. The initial spores carried from naturally contaminated field soil on the dead tissues could germinate and produce massive numbers of new spores on bulbs stored at average climatic conditions of Sudan (23–39°C, 29–93% relative humidity). Under laboratory-controlled conditions, optimal growth occurred at 75–85% r.h. on bulbs with dry scales and maximum losses occurred at 100% r.h. and ambient temperature. Underin vitro conditions, the optimal growth and sporulation temperature forA. niger was in the range of 30–35°C. Early harvesting and removal of the dead onion tissues improved bulb storability in aseptic stores under low temperature and relative humidity conditions. http://www.phytoparasitica.org posting Oct. 20, 2003.     

Germination of <Emphasis Type="Italic">Gibberella zeae</Emphasis> ascospores as affected by age of spores after discharge and environmental factors

The effects of age of ascospores (0–18 days after discharge), photon flux density (0–494 mol m^–2 s^–1 PAR), temperature (4–30 °C), frost (–15 °C for 30 min), relative humidity (RH; 0–100%), pH (2.5–6.5) and dryness (0 and 53% RH for up to 40 min) on the germination of the ascospores of the mycotoxin-producing fungus Gibberella zeae (anamorph Fusarium graminearum) were studied. Freshly discharged ascospores germinated within 4 h at 20 °C and 100% RH. The rate of germination and the percentage of viable ascospores decreased over time after the spores were discharged from perithecia. The time course of ascospore germination was not significantly affected by photon flux density. The period of time required to obtain 50% germinated ascospores at 100% RH was 26.90 h at 4 °C, 10.40 h at 14 °C, 3.44 h at 20 °C and 3.31 h at 30 °C. There was no significant effect of frost on the percentage of viable ascospores. A small percentage (6.6 ± 3.8%) of the ascospores germinated at 53% RH. At RH 84% and 20 °C almost 100% of the freshly discharged ascospores germinated. The time course of ascospore germination was affected by pH. The maximum rate of ascospore germination was estimated to be at pH 3.76. Ascospores lost their ability to germinate following exposure to 0% RH almost instantaneously. No germinating spores were detected after an incubation period of 1 min at 0% RH. Incubating the ascospores at 53% RH decreased the percentage of viable spores from 93 to 6% within 10 min. The data demonstrate that age of spores, relative humidity, temperature and pH, but not photon flux density, are key factors in germination of G. zeae ascospores.     

高温高湿对黄瓜黑星病菌孢子萌发及侵染的影响

 采取温湿度相结合的方法来研究高温处理对黄瓜黑星病菌(Cladosporium cucumerinum Ell.and Arth.)侵染的影响,比较研究了35~50℃ 4个温度梯度、50%~90% 5个湿度梯度组合处理对病菌的致死作用。同一相对湿度下,随着温度的上升病菌的致死率增加,病菌致病力降低;在同一温度下随着湿度的不断升高,受处理的孢子萌发率和致病能力都逐渐下降。在RH 80%以上、温度40℃以上时,对孢子的致死率随着处理时间的延长而增高,此高温高湿处理病菌超过2 h,病菌孢子不萌发,也基本没有接种发病率。通过高温控制苗期黄瓜黑星病的研究,初步确定高温高湿防治苗期黄瓜黑星病的最佳温度区间为40℃ 2 h或45℃ 1h (RH 80%)。     

Influence of environmental factors on field concentrations of<Emphasis Type="Italic">Alternaria solani</Emphasis> conidia above a South African potato crop

Trends in weather variables and concentrations of airborne conidia ofAlternaria solani were monitored in a potato field in South Africa during three potato-growing seasons in 2001 and 2002. Distinct seasonal variation was noted, with a drop in spore numbers during winter. Peaks in spore concentration coincided with periods favorable for spore formation and dispersal; most notable was the effect of interrupted wetting periods. Diurnal periodicity of spore dispersal was also observed, with the peak of spore concentrations between 9h00 and 18h00. Few spores were sampled at night, when wind velocity and temperature are lowest and relative humidity is highest. Increased numbers of spores were sampled during days of harvesting or when other ground-operated farm equipment was used. The results obtained in this study will be useful in establishing decision support systems to control early blight on potatoes in southern Africa. http://www.phytoparasitica.org posting July 10, 2003.     

Temporal spore dispersal patterns of grapevine trunk pathogens in South Africa

Trunk disease pathogens of grapevines, viz. Phaeomoniella chlamydospora, Eutypa lata and several species in Botryosphaeriaceae, Phaeoacremonium and Phomopsis are known to infect fresh pruning wounds by means of air-borne inoculum released after rainfall or prolonged periods of high relative humidity. Recent surveys have demonstrated that most or all of these pathogens are present in climatically diverse grape growing regions of South Africa. However, the factors controlling spore dispersal of these pathogens in vineyards were largely unknown. To address this question, spore trapping was done in a Chenin Blanc vineyard in the Stellenbosch area, South Africa, for 14 weeks during the grapevine pruning period from June to mid-September of 2004 and 2005. Hourly recordings of weather data were done by a weather station in the row adjacent to the spore trap. Spores of E. lata and Phomopsis and species in Botryosphaeriaceae were trapped throughout the trapping periods of 2004 and 2005, with higher levels of trapped spores recorded in 2005. The spores of all three pathogens were trapped during or after periods of rainfall and/or high relative humidity. In neither of the 2 years were spores of Pa. chlamydospora or Phaeoacremonium spp. trapped. Results indicated that spore event incidence, as well as the amount of spores released during a spore event of above-mentioned pathogens, were governed by rainfall, relative humidity, temperature and wind speed prior to and during the spore events.     

Spore Release of Bremia lactucae on Lettuce Is Affected by Timing of Light Initiation and Decrease in Relative Humidity

ABSTRACT A suction-impaction mini-spore trap was developed to study the effect of light initiation and decreasing relative humidity (RH) on spore release of Bremia lactucae in a controlled environment. Three light periods (from 0400 to 1600, 0600 to 1800, and 0800 to 2000 h, circadian time) at a constant RH of 99 to 100% were used for studying the effect of light initiation on spore release. Few spores were released during the dark periods. Spore release increased sharply after the initiation of the three light periods, reached a maximum 1 to 2 h after light initiation, and then declined until only a few spores could be detected. The effect of reduction in RH on spore release was studied by comparing decreases in RH 2 h before and 2 h after light initiation at 0800 h. When RH decreased from 100 to 94% 2 h before light initiation, spore release increased within 1 h, followed by a second increase after light initiation. When RH decreased 2 h after light initiation, spore release continued to increase after the initial increase after light initiation, reached a maximum 1 h after the reduction in RH, and then declined. The results suggest that both light initiation and reduction in RH can trigger spore release and that these factors have separate effects on spore release of Bremia lactucae.     

Relationship between Concentrations of Botrytis Cinerea Conidia in Air, Environmental Conditions, and the Incidence of Grey Mould in Strawberry Flowers and Fruits

Atmospheric concentrations of Botrytis cinerea conidia were monitored for two seasons in a strawberry crop in Moguer (Huelva, southwestern Spain). Concentrations of conidia were estimated using a Burkard volumetric spore sampler. A diurnal pattern of conidial release was observed. Airborne conidial concentration was significantly and positively correlated with the average solar radiation and mean temperature, and negatively with rainfall and relative humidity. Among the weather variables considered, solar radiation showed the most consistent results in the regression analysis, explaining over 40% of airborne conidial concentration variability. Correlation between Botrytis fruit rot incidence and accumulated number of conidia over seven days was significant and positive. Two regression models containing three variables explained over 62 and 52% of the fruit rot incidence variability. A positive but non-significant correlation was established between B. cinerea incidence in flowers and airborne conidial concentration. It was not possible to fit a consistent regression model to relate flower infection incidence to conidial concentration or weather variables.     

On light-sensitivity in germinating uredospores of wheat brown rust

Experiments consisted of three phases: spore production, spore storage and spore germination. Throughout the experiments temperature was near-optimal. In each phase various light and humidity treatments were given. The time at which a spore germinated was considered to be a stochastic variable. 3,000 lux inhibits germ tube elongation measurably; 7,600 lux inhibits germination measurably. Spores produced in darkness are more sensitive to light than spores produced in light, independent of the age of the pustules. Hydration of spores during storage increases light-sensitivity during germination. Samples of spores formed in darkness at low humidity are considered to consist of three sub-populations: a light-insensitive one presumably having profited from the foregoing light period, a light-sensitive sub-population and a group of spores which is inert or dead. The light-inhibited spores germinate rapidly after being placed in darkness with a germination rate little affected by the duration of light exposure. After four hours of light-exposure a gradually increasing proportion of the light-inhibited spores is killed, which means that the reversibility of the light-inhibition is limited.     

The influence of inoculum concentration, relative humidity, and temperature on infection of greenhouse tomatoes by Botrytis cinerea

Botrytis cinerea causes serious crop losses in greenhouse tomato crops through infection of flowers and stem wounds. Experiments were carried out to determine the effects of inoculum concentration, relative humidity (RH), and temperature at these two infection sites. Infection of permanent flower parts increased as a function of inoculum concentration and both length of exposure to high RH (approximately 100% for 0–36 h) and specified continuous RH (56–100%). A low level of infection was still evident under continuous 56% RH. Interruption of periods of high RH with breaks of low RH did not reduce infection. Infection of stem wounds was less dependent on inoculum concentration or RH. Factorial combinations of inoculum concentration, RH, and temperature produced significant interactions. Higher temperature increased infection of flowers but reduced infection of stem wounds. The main implications for control in commercial crops are as follows. Lowering the aerial spore concentration by maintaining the disease at a low level will reduce flower infection. Lowering RH will reduce but not eliminate flower infection but will have only a small effect on stem infection. Raising the temperature (from 15 to 25°C) will reduce stem infection, and whilst flower infection increases, this is counteracted by increased flower production and a decrease in the proportion of infections reaching the peduncle and stem.     

The spore coat of the bean anthracnose fungus Colletotrichum lindemuthianum is required for adhesion, appressorium development and pathogenicity

The spores (conidia) of the bean anthracnose fungal pathogen, Colletotrichum lindemuthianum, adhere to the aerial parts of plants to initiate the infection process. In previous studies we have shown that the Colletotrichum spores are surrounded by a fibrillar spore coat, comprising several major glycoproteins. Previous evidence showed that a monoclonal antibody (UB20) that recognised these glycoproteins was able to inhibit adhesion of spores to a hydrophobic surface. In this paper we have further studied the role of the spore coat in adhesion, germination and fungal development by studying the effects of UB20 and protease treatment of spores. The latter treatment has previously been shown to remove the spore coat. Spores germinate on glass, polystyrene and water agar, however, appressoria only develop on glass or polystyrene, showing a requirement for a hard surface. Removal of the spore coat with protease inhibits adhesion at 30 min, before the secretion of ECM glycoproteins. Protease treatment also inhibits the development of appressoria and reduces pathogenicity on leaves. Incubation of spores with the MAb UB20 inhibits adhesion at 30 min, but does not affect appressorium formation or pathogenicity. The results suggest that an intact spore coat has two functions; it is required for adhesion to a hydrophobic surface and for the detection of a hard surface necessary for appressorium formation. We suggest that contact with a hard surface, rather than adhesion, is the key event leading to appressorium formation.     

Effects of temperature and humidity on the survival of urediniospores of gladiolus rust (<Emphasis Type="Italic">Uromyces transversalis</Emphasis>)

Uromyces transversalis is an autoecious microcyclic rust mainly infecting Gladiolus spp. The pathogen is considered of plant quarantine importance in Europe and the USA. In 2006, the pathogen was found for the first time in the USA in several commercial nurseries in Florida and California. The US Department of Agriculture (USDA) initiated an eradication programme that recommended the immediate removal and destruction of infected plants followed by a host-free period, use of a fungicide treatment schedule, and equipment decontamination. In support of this plan, a study was conducted to determine how long urediniospores of U. transversalis would continue to germinate at temperatures of 2.8, 15.0, 18.8 and 25.0°C under controlled relative humidities (RH) of 11, 23, 43, 75, 93 and 100%. Choice of temperature and humidity parameters were mostly based on historical multi-year climate data from areas where the disease was detected in California and Florida. Analysis of variance (ANOVA) indicated no significant effect of RH on urediniospore germination but a highly significant effect of temperature. No germinating urediniospores were detected after 79 days for any treatment, but the 15°C treatment was more likely to be the result of germination independent of any low or high temperature-induced spore quiescence. Thus, lack of germination after 79 days was probably a good indicator of the lack of viable spores after this time for the 15°C treatment.     

Sprinkler irrigation and plant disease under semi-arid climatic conditions1

The effect of overhead irrigation on plant disease can conveniently be discussed under the following headings. Spore dispersal: irrigation effects splash dispersal and provides the necessary moisture. Under semi-arid conditions, spore dispersal takes place during the morning hours. Irrigation early in the day will aid spore dispersal. Spore resistance: irrigation will modify microclimatic conditions and reduce the stress of exposed spores to radiation, heat and dryness. Moisture period required for infection: leaf surface temperatures will determine the moisture period required for infection. Irrigation timing in relation to moisture provided by rainfall or dew may be critical. The macroclimate: the less favourable the macroclimate, the greater is the importance of microclimatic modifications, and its effect on epidemiology. Microclimatic modifications: the lower the relative humidity during the day and the shorter the period of leaf wetness (dew), the greater will be the impact of sprinkling. Foliar density interacts in determining the microclimate. The later the spore dispersal during the morning, the smaller will the effect of sprinkling be. The greater the resistance of the spores to stress conditions during the day, the smaller the effect of sprinkling. The shorter the period required for host penetration, the more pronounced will be the effect of overhead irrigation.     

Effects of temperature, relative humidity and duration of wetness period on germination and infection by conidia of the pear scab pathogen (Venturia nashicola)

Experiments were conducted to determine the effects of temperature, relative humidity (RH) and duration of wetness period on in vitro germination of conidia and infection of detached pear leaves by Venturia nashicola , the causal agent of pear scab. Conidia germinated only in near-saturation humidity (RH > 97%). The final percentage germination (24 h after inoculation) at 100% RH without free water was less than half that in free water. Conidia germinated over the range of temperatures tested (5–30°C); the optimum temperature for germination was ≈21°C. Changes in percentage germination of conidia over time were fitted by logistic models at each individual temperature. Polynomial models satisfactorily described the relationships between two (rate and time to 50% of maximum germination) of the three logistic model parameters and temperature. The minimum length of the wetness period for successful infection of detached pear leaves by conidia was observed at several temperatures. The shortest length of wetness period required for infection was 7 h at 22°C. Two polynomial models fitted well the relationship between the minimum wetness duration required for infection, and temperature.     

Identification of genes expressed during spore germination of Mycosphaerella pinodes

Mycosphaerella blight, caused by Mycosphaerella pinodes, is one of the major diseases of cultivated pea (Pisum sativum L.). To isolate the genes that are up- and down-regulated during spore germination, suppression subtraction hybridization (SSH) was performed between ungerminated and germinated spores. The 232 and 128 clones from forward and reverse libraries, respectively, were collected, sequenced, and analyzed with a BLASTX homology search. About 95% of the 32 selected clones were expressed during spore germination on a paper sheet and during infection of pea leaves. We discuss the applicability of the SSH libraries for analyzing M. pinodes genes involved in the early stage of infection.     

Effect of Humidity on Development of Tomato Powdery Mildew (Oidium lycopersici) in the Glasshouse

A series of experiments was carried out over four years in a glasshouse with computer control of humidity and temperature to investigate the effect of humidity on the development of tomato powdery mildew. Four relative humidities (RHs) (80%, 87%, 90% and 95%) at constant 19°C were maintained over an eight-week experimental period during the Autumn. Disease was greatest at 80% RH and was progressively less with increasing RH to a minimum level at 95% RH on both inoculated plants, introduced to act as initial infection sources, and on adjacent uninoculated plants. The results indicate that high humidities may decrease severity of this disease in the glasshouse and may help management of this disease in the future.     

Quantification of airborne spores of <Emphasis Type="Italic">Monilinia fructicola</Emphasis> in stone fruit orchards of California using real-time PCR

The fungal pathogen Monilinia fructicola causes blossom blight and fruit brown rot of stone fruits in California. In this study, spore densities in the air were monitored in six orchard/year combinations with Burkard spore traps. A real-time PCR assay was developed to efficiently quantify the dynamics of spore density in these orchards during the growing season. Different patterns of dynamics of spore density were observed in these orchards. A linear relationship between numbers of spores counted with a compound microscope and those determined with the real-time PCR assay was obtained, using the same samples of spore traps. Spore density in five of six orchard/year combinations ranged from 0.0 to 0.05 spores l⁻¹, except for that in orchard 4, which showed much higher values of spore density in the air, as well as higher values and wider range of incidences of blossom infection and fruit rot than those in the other orchards. The results demonstrated a potential method to quantitatively determine spore inoculum potential in orchards by using a real-time PCR assay.     

A computer-controlled environmental chamber for the study of aerial fungal spore release

ABSTRACT An environmental chamber was designed to study aerial release of spores of ascomycetes and hyphomycetes, based on a device developed by C. M. Leach. Relative humidity (RH), temperature, red (660 nm) and infrared (880 nm) light, leaf wetness, wind speed, vibration, and rain events are controlled and monitored within the chamber via an RTC-HC11 real-time controller and data-acquisition system. A BASIC11 computer program is uploaded to and controls the system. The program requests values for environmental parameters that change through time according to user specifications. The controller interacts with a stepper motor, solenoids, and relay switches via a feedback system based on data received from solid-state RH, temperature, and leaf-wetness sensors. The data-acquisition system records environmental data from the chamber in RAM (random access memory) that can be downloaded to a personal computer for correlation with spore-release data. Spores released from fungal specimens on plant tissues and cultures placed in the chamber and subjected to the desired environmental conditions are collected on a continuous volumetric spore trap at an exhaust port from the chamber. The performance of the device was examined by measuring spore release of Mycosphaerella citri, Alternaria solani, and Venturia inaequalis under various environmental conditions.